Today, specification is ongoing in 3GPP for E-UTRAN (Evolved Universal Terrestrial Radio Access Network) that is the next generation of Radio Access Network (RAN). Another name used for E-UTRAN is the Long Term Evolution (LTE) Radio Access Network (RAN). A base station in this concept is called eNB (E-UTRAN NodeB). The studies also include the possibility to have an E-UTRAN base station to provide home or small area coverage for a limited number of users. The base station is termed HNB (Home eNodeB) in the LTE context but other terms exist.
In addition, development of a cellular radio system for providing home or small area Wideband Code Division Multiple Access (WCDMA) coverage for limited number of users using a small radio base station (RBS) is ongoing. Such a radio base station is providing a small coverage area, typically the home of a subscriber will provide normal WCDMA coverage for the end users and is connected to the radio network controller (RNC) typically using some kind of Internet Protocol (IP) based transmission link.
One alternative to connect the radio base station with a small coverage area to the RNC is to use fixed broadband access, e.g. some kind of a Digital Subscriber Line (xDSL) or a Cable. Another alternative is to use some kind of wireless broadband access, e.g. WiMAX.
Typically, a radio base station providing a small coverage area can for example be equipped with a WCDMA User Equipment (UE) receiver and/or a Global System for Mobile communication (GSM) UE receiver, which enables the radio base station to scan the overlaying WCDMA and GSM environment and to camp on WCDMA or GSM cells in order to read the relevant system information. A radio base station providing a small coverage area may however be deployed without a UE receiver in the radio base station.
A radio base station providing a small coverage area can be designed to be dynamically installed by the end users in a plug-and-play fashion without any operator intervention. Also, the cell created by the deployment of such a radio base station with a small coverage area may be created automatically and configured based on information provided by an UE receiver that is included in the radio base station. For example, an UE receiver of the radio base station can be set to scan the surrounding WCDMA and/or GSM environment, e.g. a number of GSM and/or WCDMA cells with related measurement information, and to report the scanned information including the relevant system information to the RNC to which the radio base station is connected to. Using the information provided from the radio base station with a small coverage area, the RNC then creates and configures the small cell.
For example, Location Area Identity, Cell Identity, Frequency, Scrambling Code and output power for the small cell can be selected and configured among many other information elements and settings. One difference between an ordinary, macro cell, and a small cell is that the location of macro cells is known and planned by the operators. The small cells, on the other hand, can be dynamically installed in any place by the end users by deployment of a radio base station with a small coverage area without any operator intervention. As a result two small cells can be installed very close to each other as the installation of small cells is not coordinated by anyone.
In one scenario two or more radio base stations having a small coverage area are deployed with overlapping coverage areas. A problem that may then arise is that a User Equipment may receive a signal from two or more radio base stations with small coverage areas, but the corresponding radio base stations may be too spaced apart to “hear” or detect each other.
This situation creates a problem as the two radio base stations with small coverage areas may be configured to use the same scrambling code and this would create disturbance in the UE receiving both these signals and trying to communicate with one of the radio base stations.